Draft shields are utilized in dip coating systems. Their purpose is to prevent air currents from impinging on the wet coating because such air currents may create non-uniformities in the coating thickness. As seen in FIG. 1, a problem with a conventional draft shield 2 defining a vertical passageway 4 is that during the dip coating process a non-vertical substrate 6 (due to for example improper chucking with a holding device 7 or interference with another object, and the like) may strike the draft shield 2 or the dip coating vessel 8, thereby causing damage to the substrate, the draft shield, and/or the dip coating vessel.
A further problem with a conventional draft shield during the dip coating process is seen in FIG. 2 where the presence of the draft shield 2 results in a vapor density gradient (the vapor coming from the coating solution 13 and the wet coating 14) composed of highest vapor density region 12 above the coating solution 13, intermediate vapor density region 10 in the passageway 4, and the lowest vapor density region 11 for the ambient air outside the draft shield 2. A substrate having a wet coating 14 when subjected to a relatively abrupt change in vapor density from intermediate vapor density region 10 to lowest vapor density region 11 may create non-uniformities in the coating thickness.
A new draft shield is needed which avoids or minimizes the above discussed problems.
Conventional draft shields and dip coating systems are described in Petropoulos et al., U.S. Pat. No. 5,725,667 and Swain, U.S. Pat. No. 5,720,815.
The present invention is accomplished in embodiments by providing a draft shield apparatus having a longitudinal axis comprising:
an open upper end section defining a substrate entry end, an open lower end section defining a substrate exit end, and a central section between the upper end section and the lower end section, the apparatus defining a passageway which extends through the upper end section, the central section, and the lower end section along the longitudinal axis to result in an upper end section inner surface, a central section inner surface, and a lower end section inner surface, wherein the passageway has a width sufficiently large to permit movement of at least a portion of a substrate through the apparatus;
wherein the upper end section inner surface is inclined towards the longitudinal axis,
wherein the lower end section inner surface is inclined towards the longitudinal axis and the lower end section inner surface extends into the passageway such that the width of the substrate exit end is smaller than the width of the substrate entry end.
There is also provided in embodiments a coating system comprising:
(a) a coating vessel defining an opening;
(b) a draft shield apparatus having a longitudinal axis which is positioned above the coating vessel opening, comprising:
an open upper end section defining a substrate entry end, an open lower end section defining a substrate exit end, and a central section between the upper end section and the lower end section, the apparatus defining a passageway which extends through the upper end section, the central section, and the lower end section along the longitudinal axis to result an upper end section inner surface, a central section inner surface, and a lower end section inner surface, wherein the passageway has a width sufficiently large to permit movement of at least a portion of a substrate through the apparatus;
wherein the upper end section inner surface is inclined towards the longitudinal axis,
wherein the lower end section inner surface is inclined towards the longitudinal axis such that the width of the substrate exit end is smaller than the width of the substrate entry end; and
(c) a coating solution disposed in the vessel that gives off a vapor which floats into the passageway defined by the apparatus, wherein the portion of the passageway defined by the upper end section inner surface is a lower vapor density region, and the portions of the passageway defined by the central section inner surface and the lower end section inner surface are a higher vapor density region.